According to what I know, one cannot play Star Spangled Banner in public without authorization. Therefore, for Jimi Hendrix to play this song during the Woodstock Music Festival in 1969, it was very controversial.In addition, this was a period when a lot of social movements were formed to protest against the Vietnam War. So, Jimi Hendrix’s performance was definitely an anti-war performance.
I believe that the audience were influenced by this performance to a point where they would also question the war and start some sort of a movement. Also, the way Jimi Hendrix plays the song some what depicts the cruelty of the war–he uses his guitar to make gun and bomb sounds–which adds to the anti-war feeling.
The Star Spangled Banner is a song meant to embed patriotic mindset, yet I can observe from the video clip that its initial intentions were totally disregarded and that the performance projects a completely different idea as mentioned above.